I would be reluctant to use Amex in any form in Europe.
Because of its higher fees, the merchants do not like it. I
have often found that when I produced my Amex card, the
merchant would see my Visa or MC cards in my wallet and
would politely ask if I would use either of them in place of
the Amex card. While a preloaded Amex card may have security
advantages, I would seek out a Visa or MC alternative.

The Europeans are not alone in this feeling. I have a friend
who owns a couple of hotels and restaurants in the U.S. He
got so sick of dealing with Amex and its fees, that he no
longer honors Amex cards. I will use my Amex card from time
to time while traveling, but its use is limited to business
expenses that I may incur.